[En-Nut-Discussion] lvttl and ttl

[Dave Warren]

Just my view, I like you am using SAM7X.

Most poeple would not use any level shifting, almost all 5V logic uses TTL 
levels, for them driving from 3.3V works just fine. If you want to use CMOS 
logic gates select 74HCT with TTL levels rather than 74HC or 40xx types. If 
you want to drive a 3.3V device from 5V and it is not tolerant of 5V then 
use zero delay bus switches, they are bidirectional. Pericom make them, also 
Fairchild.

Best regards

Dave

----- Original Message ----- 
From: "iVesWorking" <ivesworking at hotmail.com>
To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
Sent: Thursday, November 02, 2006 10:03 AM
Subject: Re: [En-Nut-Discussion] lvttl and ttl


> so from wat u mean is always better to a bus convertor ic between two off 
> the device if the target is ,
> which IC you guys normally use (prefer bidirection)?
>
> wfloh.
>
>
> ----- Original Message ----- 
> From: "Uwe Bonnes" <bon at elektron.ikp.physik.tu-darmstadt.de>
> To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
> Sent: Thursday, November 02, 2006 4:47 PM
> Subject: Re: [En-Nut-Discussion] lvttl and ttl
>
>
>>>>>>> "iVesWorking" == iVesWorking  <ivesworking at hotmail.com> writes:
>>
>>    iVesWorking> my previous design is base on avr which run 5V TTL, but i
>>    iVesWorking> looking forward on 3.3V LVTTL Sam7X, but i not sure about
>>    iVesWorking> the need on adding a 3.3V to 5V bus convertor, or just
>>    iVesWorking> connect as usual, since device mention about their are 5V
>>    iVesWorking> tolerance, so i assume using the same connection without
>>    iVesWorking> the bus convertor will be fine. is this true?
>>
>> The SAM is 5 Volt tolerant and can live with Signals coming from 5 V TTL 
>> or
>> 5 V CMOS. 5 Volt TTL is also perfectly happy with 3.3 Volt CMOS Signals, 
>> as
>> coming from th SAM7. However 5 Volt CMOS will work (if supposed to work
>> together with 5 V TTL), or may work (if the VIH Voltage in the datasheet 
>> is
>> above 3.3 Volt). 5 Volt CMOS RAM will draw substantial more idel current
>> with 3.3 Volt CMOS input voltage, as the input buffers will be somehow 
>> cross
>> conducting.
>>
>> So it depends...
>> -- 
>> Uwe Bonnes                bon at elektron.ikp.physik.tu-darmstadt.de
>>
>> Institut fuer Kernphysik  Schlossgartenstrasse 9  64289 Darmstadt
>> --------- Tel. 06151 162516 -------- Fax. 06151 164321 ----------
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>
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